The following three paragraphs have horizontal margins of 8% and text-indent of 4%. The measurements refer to the width of the parent element (the same as this paragraph), and so should be the same for all three paragraphs.
The confidence and security of a people can be measured by their attitude toward laxatives. (100% font-size)
The confidence and security of a people can be measured by their attitude toward laxatives. (130% font-size)
The confidence and security of a people can be measured by their attitude toward laxatives. (160% font-size)
The following three paragraphs have horizontal margins of 2em and text-indent of 1em. These measurements refer to the font-size of the element itself, and so should increase proportional to font-size.
The confidence and security of a people can be measured by their attitude toward laxatives. (1em font-size)
The confidence and security of a people can be measured by their attitude toward laxatives. (1.3em font-size)
The confidence and security of a people can be measured by their attitude toward laxatives. (1.6em font-size)
The confidence and security of a people can be measured by their attitude toward laxatives.
— Florence King